The overall goal of this proposal is to examine the structural and functional properties of glycogenin that lead to its unique self-glucosylation activity that primes the synthesis of glycogen. Glycogen is an important storage reserve of glucose and the mechanism by which the synthesis of glycogen is initiated and synthesized is conserved from yeast to humans. Aberrant regulation of this process is associated with various glycogen-storage diseases and Type II Diabetes. The long-range goal of this proposal is to provide both a structural context for the auto-glucosylation reaction catalyzed by glycogenin and new information with regard to the mechanism by which this unusual reaction is catalyzed. While our recent structure determination has not proven one particular mechanism over another, it does provide us with a new starting point from which to probe the specifics of catalysis, both chemically and kinetically, that underlie the initiation step of glycogen synthesis. The work described in this proposal will provide a foundation for a complete understanding of the functional and structural properties of glycogenin and will contribute new insight into the synthesis of a glycogen particle and the role that glycogenin plays in this important cellular process. During the performance of this work we will 1) Determine the three-dimensional structure of full-length glycogenin, to understand how the protein might interact with glycogen synthase. 2) Examine the structural determinants of substrate and acceptor binding by obtaining structures of the enzyme in complex with both substrate and acceptor molecules. 3) Assess the role that subunit interactions play in both the initial and subsequent phases of the glycosyltransferase reaction. 4) Test the proposed roles for specific residues in the active site of glycogenin during catalysis and for the recognition of substrate and acceptor molecules. [unreadable] [unreadable]